Superheterodyne receiver



p 7, 1949. F/A. DE G'ROOT 2,483,315

SUPERHETERODYNE RECEIVER Filed April 19 16 .FOIJKERT ALBERT 12E GROOI v IN V EN TOR.

ATTORNEY Patented Sept. 27, 1949 UNITED STATES PATENT 2,483,315 I l SUFERHETERODYNE RECEIVER Folkert Albert de Groot, Eindliov'en, Kieth 'i'land's,

a'ssignor, by mesne assi nments, t6" Hai'jtffoi'if National Bank and Trust come-an Hartford;

001111., as" trustee Application April 12', 1946, S:eri al i'sf 661,522; In the Netherlands May 3, 1943 Section 1, Public Law 690-,Ai13'i1st8, 194$ Patent eipires May 3; 1963' The present invention relates to a superheterodyne receiver, and itparticularly pertains toa sharp filter for selecting the: carrier wave inter posed in' the intermediate frequency amplifier of the receiver? and comprisimg;v one or more res= onant circuits the damping ofwhic'h is controlled by an amplifier.

In: this case the" damping. of the resonant circui-ts is. reducedby means of feed back coupling via one or more of the discharge systems belong ing to: the amplifier,. or by a negative resistance" appearing between: two electrodes at one or more of these discharge systems. The term selec'ting" is construed herein; to includethe accentuation of the carrir'wav'ewith respect to the side= band frequencies, as well as the separation or suppression of the-carrier wave.

A receiver of this' kind, for example, permits the elimination of the serious distortion which occurs when the carrier wave of the received signal is attenuated by selective fading more: strongly than are the Side-'bandsi This is en sured by utilizing a sharp filter in the receiving channel to' accentuate; the carrier wave with re=- spect to the' side-bands; Such accentuati'on ispreferably accomplished by means of a filter comprising one or' moreresonant circuits the damping 01fv which is reduced by an amplifier.-

The invention more particularly relates to a form of construction of the above de'scribed' superheterodyne receiver wherein all the side: band frequencies are attenuated at least approxi- 10 Claims. (Cl. lie-iii) mately inproportion" to the attenuation of the carrier wave;- Accor'ding to the invention, to this end the receivedintermediate frequency oscillations corresponding to the received carrier frequency and side-band frequency signals are transferred directly to the amplifier which reduces the damping of'the' resonant circuit or cir-'- cuitsof thesharpfilter, and supplied indirectly to thefilter viaithis' amplifier, while the resulting 2 gilitenoy oscillations were supplied directly to the Consequentl'y, it is also" desirable that the 0s c llat ons of intermediate-frequency corresponding to the ca rrier wave selected by the filter should be derived froin th whole of the inter- Ir ed ate treq icncy os'cillatipnsvia the amplifier, so that the camping of the following intermed ate-fregn cy circiiitdoes' not affect the filter. is the fidsisible, is true, to suppress the damp ng ce iii the iifecding and'of in cwii g freq enc'ytire ts t5; reducing the c m ing; or the inter more lf6f1l with the aid oi; ihe mpiifieigcui m pfacfiie the daifijiing oi the circuitiifduld have to te reduced to such extent tie-it me" sta i nw endangered, so that S'Glf-ifilifitidfi fof Xallfible wan smelt vans one of unaerconsmerafion;

agitate-gents circuit arrangee r in at least one stage time a g na, bo nine trite ance-frequency 0sc ll'at ohs suppli'f dire t6 the afiiplifii and git; oscillations selected t3, hie filter are am ii The fee v'ed ififrfiie'dijdtefrediiefic i} o cillation's" prei'iatiy M p I chjrir'iliii series with theoi tpiit rni filter; this series" connection being" co led" to the input electrodes of a discneigj sir camping or 1 rue interni'ai te'neqiieiics osciiittioiis ma alternat vely bet'ra sinittditc one of the controi grids or a (r sensystem with the aid or vvhi'cli' the'dai "g or the filter reacted white the output v is or the filter are connected to another con for er ancrtts' the cathode of this dis nargesystenr iespcctiveir;

since, I fulejit necessary for the damping" of the nicer to be sfirorieiy'inircea, the damp ing reducing amplifier is preferably firovided with meat eied beck} an this in siic'fi manner that qenipinetr the fi ter; not reduced y "ck" itself. step results instatility of tl'ie circuit' arrangement so that there is no an er of seir-xc'itatizijn ir'i' trie daseof's'trfig reduction of damp ng of me filtefi V o If the received inlieiiifedijf-frediiency oscillla'tio'nsf are transferred fidudtitel y to an impedance manne iii fcivi-ii'gcHannel-in series v'i'lith' the detect tei iiiii'ia'ls of: the filter, it frequeiim' OECuYS tHaf-fil accentiiatiofi of theside- 3 bands is not wholly symmetric with respect to the carrier wave.

According to a recognition which also underlies the invention, this asymmetry lis due to parasitic capacities which inay exist between the preceding intermediate-frequency circuit and the said impedance, and between the said impedance and earth. According to the: inventionthe disadvantageous consequences involyed by the occurrence of these capacitiesjare suppressed by connecting a condenser in parallel with the series-connection of the impedance and the out pu terminals of the filter and/or by the interposition or a condenser between thei npedance and the preceding intermediate-frequency"circuit, which condenser (condensers) is .(are) so.

adjusted that the influence of the said parasitic coil 8 comprises a core of high-frequency iron which has themagnetising coil l8 arranged on it. By varying the direct current flowing through the said coil it is possible for the inductance of the coil 8 and hence for the tuning of the sharp filter circuit to be varied within definite limits.

Due to the presence of the sharp filter circuit 5, the-side-band frequencies of the intermediatefrequency signal are strongly attenuated with respect to the. carrier wave, thus avoiding the danger thatwith selective fading an apparent capacities upon the resonance curve of the filter h is neutralized.

The invention will be explained more fully by reference to the accompanying drawing showing, by way of example, one embodiment thereof.

The figure shows the intermediate-frequency portion of a receiver comprising a sharp filter for the selection of the carrier wave, a control voltage for the automatic frequency control being produced with the aid of a selective network which has two control rectifiers connected to it, and the intermediate-frequency carrier wave being maintained within the range of frequencies selected by the filter due to the tuning or the sharp filter being acted upon by the said control voltage. The filter also forms part of the above-mentioned selective network.

The intermediate-frequency portion of the receiver comprises an intermediate-frequency amplifying tube i which is coupled to the control grid circuit of a discharge tube 4 via a resonant circuit 2 tuned to the intermediate-frequency and an impedance comprising a coupling coil 3. The latter is in series with a filter whichis-constituted by a circuit the damping of which is reduced and which is constituted by a condenser i3 and two series-connected coils l and 8. Consequently, the received intermediate-irequency oscillations are transferred indirectly to the filter 5. The damping of circuit 5 is reduced by being connected in three-point arrangement to the discharge tube fl. This tube'is also provided with negative feed-back by that the cathode lead in cludes a resistance 9' which is notbridged for intermediate-frequency current. Th damping of filter 5 is, however, not reduced by the presence of this resistance. The anode circuit of the discharge tube 4 includes a resonant circuit it which is tuned to the ,intermediatefrequency and which is coupled by capacitive means to a diodedetector H, th audio-frequency output voltage of which is suppliedto an audio-frequency amplifier (not shown) V f The circuit 2 has, in addition, coupled to it a circuit 12 which is'falso'tun'ed to the intermediate-frequency and which. has connected to it two pushpull connected control rectifiers (diodes) l3 and 14. The, centre of circuit [2 is connected to the centre ofthe output resistance I5 of the two diodes l3 and, i4 via a coupling coil I 5 which is inductively coupled to the intermediate-frequency circuit Ill. The circuitfi, l0 and I2 and the couplingcoil it, together with the rectifiers i3 and Id, jointly constitute a device for producing a control voltage for automatic quency control, which control voltage is proovermodulation of the signal occurs which would involve a strong non-linear distortion of the lowfrequency signal.

If, now, the intermediate-frequencysignal to be supplied to the detector stagewould-be derived solely from the filter, a veryserious linear distortion of this signal wouldresult due to the side-band frequencies being unevenly attenuated by the filter. By the use of the invention, this linear distortion of the signal is avoided almost completely. It is true that in the circuit according to the invention the side-band frequencies,

are amplified to a considerably smaller extent than the carrier wave-thisis the i purpose of the sharp filterbut all these frequencies are attenuated at least approximately to the same extent with respect tolthe-carrier wave. may be readily appreciated when the filter is imagined as short-circuited; in this case the intermediate-frequency oscillations transferred to the impedance 3 are amplified in the normal manner. circuited the oscillations selected b the filter must be added. In the resulting intermediatefrequenoy oscillations which are constituted by the sum of the selected oscillations and of the normally amplified oscillations the various sideband frequencies, apart from less important variations, are thus attenuated almost uniformly with respect to the carrier wave.

In one practical form of construction the carrier wave may thus, for example, be amplified 10 to 15 times with respect to the amplification of the side-band frequencies;

For the desired operation of the circuit arrangement it is necessary that the tuning frequency of the circuit 5 should always correspond within narrow limits to the intermediate-frequency carrier wave. This conformity is ensured by the automaticfrequency contro1 since when a deviation occurs between thesaid frequencies there is produced across the resistance 5 a control voltage of suitable polarity-whichchanges the inductance of the coil 8 to such extent that the tuning frequency of the circuit-5 isapproxirier-wave frequency.

Due to the circuit 5 forming part of the network for the production of the control voltage, the control is highly sensitive to small variations in frequency.

The coupling 'coil 3 iscoupled to the intermediate-frequency circuit 2 not only inductively but also by capacitative means via a variable condenser 19. In additionavariable condenser 2&2 is connected in parallel with the series-connect1on of the coupling coil 3 and the circuit 5. The parasitic capacities which exist between the inmately brought again in conformity with the car;

If, however, the filter is not short-.

termediate frequency circuit 2 and the coil 3 and between the coupling coil 3 and earth respectively are connected in parallel with the condensers l9 and 23 respectively. When the condensers l9 and 26 were not present, these parasitic capacities could bring about asymmetry in the resonance curve of the filter so that the lateral hands would no longer be symmetrically attenuated With respect to the intermediate-frequency carrier wave.

According to the invention, this influence of the parasitic capacities on the resonance curve is neutralizedby the arrangement of condensers l9 and 2E. of at least one of these condensers it is possible to obtain a filter exhibiting a symmetric resonance curve, due to which distortion of the signal is avoided. v

What I claim is:

1. An amplifier circuit arrangement, particularly for use in a receiver for receiving signal voltages of carrier and sideband frequencies, comprising an am lifier having an input circuit and an output uliClllt, filter circuit elements sharply tuned to a frequency corresponding to said carrier frequency, means to apply a first signal voltage having frequency components corresponding to said carrier and said sideband frequencies to the input circuit of said amplifier, means to couple said filter circuit elements to said amplifier to derivea second signal voltage of frequency corresponding to said carrier frequency,.means to apply said second si nal voltage to the input circuit of said amplifier and to reduce the damping of said filter, and means coupled to. the output circuit of said amplifier to derive an output voltage comprising said first signal voltage and said second signal voltage.

2.- An amplifier circuit arrangement, particularly for use ina receiver forreceiving signal voltages of carrier and sideband frequencies, comprising a resonant circuit for translating a first signal voltage having frequeiicy components corresponding to said carrier and said sideband frequencies, an amplifier having an input circuit and an output circuit, filter circuit elements sharply tuned to a frequency corresponding to said carrier i'requency,=means to couple said resonant circuit to the input circuit ofsaid amplifier to apply a signal voltage of frequency corresponding to said carrier and sideband frequencies to said amplifier, meansto couple said filter circuit elements to said amplifier to derive a second signal voltage of frequency corresponding to said carrier frequency, means to apply said second signal voltage to the input circuit of said amplifierand to reduce the damping of said filter, and means coupled to the output circuit of said amplifier to derive an output voltage comprising said first signal voltage and said second signal voltage.

3. An amplifier circuit arrangement, particularly for use in a receiver for receiving signal voltages of carrier and sideband frequencies, comprising a. resonant circuit for translating a first signal v -tage having frequency components corresponding to said carrier and said sideband frequencies, an amplifier having an input circuit and an output circuit, a filter circuit sharply tuned to a frequency corresponding to said carrier frequency Ts-cans to couple said resonant circuit and said filter circuit in series to the input circuit of said amplifier to apply a signal voltage of frequency corresponding" to said carrier and sideband frequencies to said amplifier, means to By means of a suitable adjustment 6 couple said filter circuit to said amplifier to derive and apply to theinput circuit of said amplifier a second signal voltage'of frequency corresponding to said carrier frequency to reduce the damping of saidfilter,- and means coupled to the output circuit of said amplifier to derive an output voltage coniprising'said first signal voltage and saidsecond signal voltage and having carrier frequency components relative to sideband fre quency components greater than the carrier frequency component of said first signal voltage.

d. An amplifier-circuit arrangement, particularly for use in a receiver for receiving signal voltages of carrier and sideband frequencies, comprising a resonant circuit for translating a first signal voltage having frequency components corresponding to said carrier and said sideband frequencies, an electron discharge tube amplifier having a cathode, a first control grid, ascoond control grid and an anodeyafilter circuit tuned to frequency corresponding to carrier frequency, means to couple said reson nt ircuit to the first control grid of said amplifier tulle to. apply 'a signal voltage of frequency corresponding to said carrier and sidehe frequencies to said amplifier, means to =.euple filter to said amplifier tube to derive al tage of frequency correspondcarrier frequency, means to apply said r l voltage to the secondcontrol grid er tube and to reduce the damping d meanscoupled to the anode of we to derive an output voltage g first signal voltage and said sec- 0nd voltage and. having carrier frequency c-s'nponents relative tosideloand: frequenc components greater than the carrier frequency cornponent of said first signal voltage.

5. An amplifier circuit arrangement, particularly for use in a receiver for receiving signal voltages of carrier and sideband frequencies, comprising a resonant circuit for translating a first signal voltage having frequency components corresponding to said carrier and said sideband frequencies, an amplifier having an input circuit and an output. circuit, 'a filter circuit sharply tuned to a frequency corresponding to said carrier frequency, means to couple said resonant circuit to the input circuit of said'amplifi'er to apply a signal voltage of frequency correspond ing to said carrier and sideband frequencies to said amplifier, means to couplesaid' filter circuit to said amplifier to derive a second signal voltage of frequency corresponding to said carrier frequency, means to apply said second signal voltage to the input circuit of said amplifier and to reduce the damping of said filter, means to couple the output circuit of said amplifier to the input thereof to apply negative feedback thereto and to prevent said negative feedback from reducing the damping of said filter circuit, and. means coupled to the output circuit of said amplifier to derive an output voltage comprising said first signal voltage and. said second signal voltage and having carrier frequency components relative to sideband frequency components greater than the carrier frequency component of said first signal voltage.

6. An amplifier circuit arrangement, particularly for use in a receiver for receiving signal voltages of carrier and sideband frequencies, comprising a first amplifying stage, a resonant circuit for translating a first signal voltage having frequency components corresponding to said carrier and said sideband frequencies inductively coupled to said first amplifying stage, a first capacitor coupling said resonant circuit and said first amplifier stage, an amplifier having an input circuit and an output circuit, a filter circuit sharply tuned to a frequency corresponding to said carrier frequency, means to couple said resonant circuit and said filter circuit in series to the input circuit of said amplifier to apply a signal voltage of frequency corresponding to said carrier and sideband frequencies to said amplifier, a second capacitor connected in parallel with said series connected resonant circuit and said filter circuit, means to couple said filter circuit to said amplifier to derive and apply to the input circuit of said amplifier a second signal voltage of frequency corresponding to said carrier frequency to reduce the damping of said filter, and means coupled to the output circuit of said amplifier to derive an output voltage comprising said first signal voltage and said second signal voltage and having carrier frequency components relative to sideband frequency components greater than the carrier frequency component of said first signal voltage, said first and said second capacitors having capacity values at which the influence of the parasitic capacities between said first amplifying stage and said resonant circuit and said filter circuit are neutralized.

'7. An amplifier circuit arrangement, particularly for use in a receiver for receiving signal voltages of carrier and sideband frequencies, comprising a resonant circuit for translating a first signal voltage having frequency components corresponding to said carrier and said sideband frequencies, an amplifier having an input circuit and an output circuit, a filter circuit, means coupled to said resonant circuit and the output circuit of said amplifier automatically to tune said filter sharply to a frequency corresponding to said carrier frequency, means to couple said resonant circuit to the input circuit of said amplifier to apply a signal voltage of frequency corresponding to said carrier and sideband frequencies to said amplifier, means to couple said filter circuit elements to said amplifier to derive a second signal voltage of frequency corresponding to said carrier frequency, means to apply said second signal voltage to the input circuit of said amplifier and to reduce the damping of said filter, and means coupled to the output circuit of said amplifier to derive an output voltage comprising said first signal voltage and said second signal voltage.

8. An amplifier circuit arrangement, particularly for use in a receiver for receiving signal voltages of carrier and sideband frequencies, comprising a first amplifying stage, a resonant circuit for translating 3, first signal voltage having frequency components corresponding to said carrier and said sideband frequencies inductively coupled to said first amplifying stage, a first capacitor coupling said resonant circuit and said first amplifier stage, an amplifier having an input circuit and an output circuit, a filter circuit, means coupled to said resonant circuit and to the output circuit of said amplifier automatically to tune said filter circuit sharply to a frequency corresponding to said carrier frequency, means to couple said resonant circuit and said filter circuit in series to the input circuit of said amplifier to apply a signal voltage of frequency corresponding to said carrier and sideband frequencies to said amplifier, a second capacitor connected in parallel with said series connected resonant circuit and said filter circuia means to couple said filter circuit to said amplifier to derive and apply to the input circuit of said amplifier a second signal voltage of frequency corresponding to said carrier frequency to reduce the damping of said filter, and means coupled to the output circuit of said amplified to derive an output voltage comprising said first signal voltage and said second signal voltage and having carrier frequency components relative to sideband frequency components greater than the carrier frequency component of said first signal voltage, said first and said second capacitors having capacity values at which the influence of the parasitic capacities between said first amplifying stage and said resonant circuit and said filter circuit are neutralized.

9. An intermediate frequency amplifier circuit arrangement, particularly for use in a superheterodyne receiver for receiving signal voltages of carrier and sideband frequencies, comprising a resonant circuit for translating a first intermediate frequency signal voltage having frequency components corresponding to said carrier and said sideband frequencies, an electron discharge amplifier tube having a cathode, a control grid and an anode, a filter circuit comprising a first capacitor connected in parallel with a first inductor and a second inductor connected in series, means to couple said resonant circuit and the first inductor of said filter circuit in series between the control grid and cathode of said amplifier tube to apply a signal voltage of frequency corresponding to said carrier and sideband frequencies to said amplifier, means to couple said filter circuit to the cathode of said amplifier tube to apply to the control grid of said amplifier tube a second intermediate frequency signal voltage of frequency corresponding to said carrier frequency to reduce the damping of said filter circuit, means coupled to the anode of said amplifier tube and to said resonant circuit to derive a frequency control voltage, a third inductor coupled to the second inductor of said filter circuit, means to apply said frequency control voltage to said third inductor to tune said filter sharply to an intermediate frequency corresponding to said carrier frequency, and means coupled to the anode of said amplifier tube to derive an output voltage comprising said first intermediate frequency signal voltage and said second intermediate frequency signal voltage and having carrier frequency components relative to sideband frequency components greater than the carrier frequency component of said first intermediate frequency signal voltage.

10. An intermediate frequency amplifier circuit arrangement, particularly for use in a superheterodyne receiver for receiving signal voltages of carrier and sideband frequencies, comprising a resonant circuit for translating a first intermediate frequency signal voltage having frequency components corresponding to said carrier and said sideband frequencies, a first electron discharge amplifier tube having a cathode, a control grid and an anode, a filter circuit comprising a first capacitor connected in parallel with a first inductor and a second inductor connected in series, means to couple said resonant circuit and the first inductor of said filter circuit in series between the control grid and cathode of said first amplifier tube to apply a signal voltage of frequency corresponding to said carrier and sideband frequencies to said amplifier, means to couple said filter circuit to the cathode of said amplifier tube to apply to the control grid of said first amplifier tube a second intermediatefrequency signal voltage of frequency corresponding to said carrier frequency to reduce the damping of said filter circuit, a negative feedback resistor interposed between the first inductor of said filter circuit and the cathode of said first amplifier tube, a frequency responsive detector circuit coupled to the anode of said amplifier tube and to said resonant circuit to derive a frequency control voltage, a third inductor electromagnetically coupled to the second inductor of said filter circuit, a second electron discharge tube amplifier to apply said frequency control voltage to said third inductor automatically to tune said filter sharply to an intermediate frequency corresponding to said carrier frequency, and means coupled to the anode of said first amplifier tube to derive an output voltage comprising said first intermediate REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 15 2,162,988 Wright June 20, 1939 2,256,070 Weagant Sept. 16, 1941 

